A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
In commercial lithographic apparatus, for example steppers and scanners, it is often necessary to move the substrate and/or patterning device within the lithographic apparatus. For instance, in a scanner the substrate and the patterning device may be moved simultaneously and in opposite directions in order to apply a pattern to the substrate. In a stepper, the substrate will need to be moved so that different target portions of the substrate can be exposed to radiation. It is desirable to ensure that the throughput of a lithographic apparatus is as high as possible. In order to maximize throughput, it is often necessary to move the substrate and/or patterning device as fast as possible from a first position to a second position. For example, the first position of the substrate may be such that a first target portion of the substrate is in position to be exposed to a radiation beam, and a second position may be when a second target portion of the substrate is arranged to be in position to be exposed to a radiation beam. In order to move the substrate and/or patterning device as fast as possible, the acceleration of the substrate and/or patterning device will be high. The higher the acceleration of the substrate and/or patterning device, the higher the (accelerating) force acting on the substrate and/or patterning device and apparatus holding the substrate and/or patterning device.
In an existing lithographic apparatus, the lithographic apparatus comprises an arrangement for holding a substrate in position, for example a substrate support structure. The arrangement may comprise two parts: a first part which holds the substrate, and a second part which holds or supports the first part. The first part is often referred to as a wafer table, and second part is often referred to as a chuck or mirrorblock. The first part and the second part may be clamped together using a vacuum clamp arrangement. As discussed above, the arrangement may undergo high acceleration. Such high acceleration can cause the first part of the arrangement to slip relative to the second part of the arrangement, or cause distortion in one or both of the parts. Such slip or distortion can result in the substrate, and therefore target portions of the substrate, being misaligned with respect to the radiation beam. Such misalignment can cause patterns to be inaccurately applied to the substrate, and if the misalignment is not consistent when patterns are overlaid on top of one another, overlay errors can also arise.
Similarly, in an existing lithographic apparatus, the lithographic apparatus comprises an arrangement for holding a patterning device in position, for example a patterning device support structure. The arrangement may comprise two parts: a first part which holds the patterning device, and a second part which holds or supports the first part. The first part and the second part may be clamped together using a vacuum clamp arrangement. The patterning device support arrangement may also undergo high acceleration, for example in a scanning lithographic apparatus. Such high acceleration can cause the first part of the arrangement to slip relative to the second part of the arrangement, or cause distortion in one or both of the parts. Such slip or distortion can result in misalignment of the patterning device, and therefore misalignment of patterns applied to target portions of the substrate.
It is desirable to provide, for example, a support structure, a lithographic apparatus and method that obviates or mitigates one or more of the problems of the prior art identified above.